関東山地秩父帯の上吉田ユニットの地質年代

概要

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Late Early to early Middle Jurassic radiolarians were first recovered from the Kamiyoshida unit in the northern part of the Chichibu belt, Kanto mountains, central Japan. The unit has been regarded as Middle to Late Jurassic age. The late Early to early Middle radiolarians identified are as follows : Laxtorum (?) jurassicum ISOZAKI and MATSUDA, Laxtorum (?) hichisoense ISOZAKI and MATSUDA, Hsuum cf. fukazawaense SASHIDA, Hsuum aff. hisuikyoense ISOZAKI and MATSUDA, Canoptum sp., Parahsuum simplum YAO. The unit contains also Middle to early Late Jurrassic radiolarinas such as Parvicingula dhimenaensis BAUMGARTNER, Stichomitra (?) takanoensis AITA, Dictyomitrella (?) kamoensis MIZUTANI and KIDO, Sethocapsa yahazuensis AITA, Sethocapsa cf. funatoensis AITA, Stichocapsa convexa YAO, Stichocapsa japonica YAO, Eucyrtidiellum unumaense YAO, Tricolocapsa convexa MATSUOKA. In the northern Chichibu belt, the former radiolarians occur from the northern part of the Kamiyoshida unit, while the latter younger ones are found from the southern part of the unit. The older part of the unit, chaotic sediments including melange, is biostratigraphiccally correlated to the Kazahaya-toge unit consisting of the turbidite sequence, one of the tectonic units of the northern Chichibu belt. These evidences suggest that the formation of accretionary complex of the Chichibu belt has commenced in early Jurassic.
国立科学博物館の論文
1994-12-22